Alloy characterized by controlled thermoelasticity at elevated temperatures



7, 1964 H. L. EISELSTEIN ETAL 3,157,495

ALLOY CHARACTERIZED BY CONTROLLED THERMOELASTICITY AT ELEVATED TEMPERATURES Filed Oct. 22, 1962 2 Sheets-Sheet 2 ,(olvsnbaaj JUN/09% United States Patent 0" rate Oct. 22, 1962,5enNo. zsaess 22 Qlaims. or. 75-134 The present invention relates to novel iron-nickelcobalt-columbium alloys, and more particularlyto age hardenable iron-nickel-cobalt-columbium alloys which, in the hardened condition, exhibit a controlled thermoelastic coeflicient and a high level of strength over a Wide range of temperature.

It has been well known that most metals and alloys are characterized by variations in Youngs modulus of elasticity with variations in temperature, this characteristic being known as thermoelasticity and the proportionate change in the modulus per unit change in temperature has been known as the temperature coefficient of Youngs modulus of elasticity. The most common type of thermoelasticity is a decrease in Youngs modulus with an increase in temperature, i.e., the temperature coeificient of Youngs modulus is negative. The primary result of a decrease in modulus of elasticity is a reduction in n'gidity of the structure and an increase of deflection under load as the temperature increases. More specifically, resilient elements such as vibratory reeds, mechanisms and springs made of usual alloys and employed in operation over a range of temperatures undergo changes in essential characteristics, e.g., vibratory reeds suifer a change in resonant frequency, and springs no longer exert the same force when deflected a given amount. These elfects of temperature upon the modulus of elasticity pose difficult problems in the design of equipment which must operate throughout a range of temperature, thereby limiting the accuracy and/or the operating temperature range of such equipment. .The problems are further complicated when the variation of the modulus with temperature is not substantially uniform, thus increasing the difficulty and/ or limiting the accuracy of measures to compensate for variations in the modulus.

One means of overcoming the disadvantages of thermoelasticity is to use special alloys which have thermoelastic characteristics specially adapted for particular situations, if such special alloys are available. Thus, where it is desired that the rigidity of a structure be constant throughout a range of temperatures, it is advantageous to make the structure of an alloy characterized by a temperature coefiicient of Youngs modulus equal to zero throughout that range of temperature. If it is desired that the rigidity of a structure increase with an increase in its operating temperature, then it is advantageous that the structure be made of an alloy having a temperature coefficient of Youngs modulus greater than zero, i.e., of positive value, throughout that range of operating temperatures. I

in the design of vibrating mechanisms and springs, the combined effect of thermoelasticity and thermal expansion is frequently of primary concern, rather than the efiect of thermoelasticity alone, since dimensional changes resulting from thermal expansion also affect the behavior of such articles. A coefiicient known as the thermoelastic coefiicient (T.E.C.) is employed to characterize the combined effects of thermoelasticity and thermal expansion, the therrnoelastic coefiicient being the algebraic sum of the temperature coeflicient of Youngs modulus of elasticity plus the temperature coefiicient of linear expansion. Where it is desired that an elongated ice element of uniform cross section have a constant resonant frequency throughout a range of temperatures when vibrating in the manner of a tuning fork, it is advan tageous that the element be made of an alloy having a thermoelastic coefiicient equal to zero throughout that range of temperatures. .Also, where it is desired that a spring have constant deflection per unit load throughout a range of temperatures, it is advantageous that the spring be made of an alloy having a thermoelastic coefiicient of zero throughout that range of temperatures. In other situations, such as those requiring compensation for other effects of temperature, it is advantageous that the thermoelastic coefiicient be a positive or negative value throughout the range of operating temperatures and that the thermoelastic coefiicient be uniform, i.e., that the variation of modulus with temperature be uniform.

Alloys which are produced under one or more 'spe cial controls which provide that the finished alloy be characterized by a thermoelastic coefiicient approximately equal to a preselected value are referred to as being characterized by a controlled thermoelastic coefficient. These special controls include control of the composition, control of the heat treatment and control of the amount of cold working of the alloy.

In the past, adverse effects of temperature variations upon elasticity have been largely avoided by use of alloys which maintain a controlled thermoelastic coefficient up to temperatures of about 350 F. However, recent developments in todays rapidly expanding technology have resulted in the need for alloys possessing an advantageously controlled thermoelastic coefi'icient up to substantially higher temperatures in order that measuring and controlling equipment, devices, systems, etc., will operate satisfactorily and in order that such structures will maintain their rigidity at elevated temperatures.

It is also well known that the tensile strength and other mechanical characteristics of many metals and alloys deteriorate upon exposure to elevated temperatures. These may be either reversible changes whereby the original characteristics are regained upon cooling to room temerature, or irreversible changes resulting from a different metallurgical structure being formed when the alloy is heated and cooled. In less frequent instances, an alloy may gain strength but suffer a loss in ductility, for example, by excessive age hardening or by undergoing a phase transformation while in service at the elevated temperature. In any of these cases, the deterioration in mechanical properties due to exposure to elevated temperature is frequently deleterious to the performance of equipment which must operate throughout a range of temperatures and it is advantageous that alloys for such equipment be resistant to these effects of exposure to elevated temperatures.

It is also important that structural alloys have characteristics permitting them to be readily fabricated by economical methods. Such alloys should be malleable in the hot state, and be suitable for cold forming, brazing and Welding. Also, the requisite mechanical properties must be attainable by relatively simple heat treatments, and unusually difiicult operations such as very high degrees of cold working should not be necessary. Furthermore, the alloys should not contain large amounts of readily oxidizable elements which can cause difficulties in casting or promote rapid oxidation during service at elevated temperatures.

In some instances, alloys have been designed to retain a constant modulus of elasticity over a very limited range of temperatures, and other alloys have been developed which retain high levels of strength at elevated temperature. However, where operating temperatures range from room temperature or lower up to about 600 F. or higher, metallic structures made of known alloys are subject to either or both of the detrimental effects of substantial variations in modulus of elasticity, and/or low tensile strength. Although many attempts were made to overcome the foregoing dificulties and other disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

Alloys have now been discovered containing especially correlated amounts of nickel, cobalt, iron and columbium which, in the age hardened condition, have an advantageous combination of properties including controlled thermoelastic coefficients and high levels of strength over a relatively wide range of temperatures. These new alloys canbe readily fabricated by casting, hot working, cold working, brazing or welding, and, when age hardened, are metallurgically stable at temperatures up to at least 900 F.

It is an object of the present invention to provide ferromagnetic alloys characterized by substantially uniform and controlled thermoelastic coefiicients and high strength were wide range of temperatures.

Another object of the invention is to provide alloys which can be processed by heat treatment with the option of cold working to be characterized by high strength and by substantially uniform thermoelastic coefiicients controlled to be approximately equal to any required value from about minus 50x10 F. to about plus 125' 10 /F. throughout the temperature range of from about room temperature to at least about 600 F. by control of alloy composition and heat treatment either with or without cold working.

- The invention also contemplates providing alloys characterized by ferromagnetism and by thermoelastic coefficients which are controlled to be about equal to any required value from about minus 50 10- F. to about plus 125 10- F., throughout the temperature range from about 80 F. up to at least about 600 F.

his a further object of the invention to provide an alloy which undergoes only a very moderate change in modulus of elasticity and retains a high level of strength when heated in the temperature range from room temperature or lower to up to at least about 600 F.

The invention further contemplates providing an age hardened alloy which retains a high level of strength and is metallurgically stable when repeatedly heated and cooled throughout the temperature range of about 80 F. to 900 F.

ItVis another object of the invention to provide a process for heat treating, with the option of cold working, the alloy of the presentinvention which will result in said alloy having a controlled thermoelastic coefiicient approximately equal to any required value in the range from about minus 50X 10 F. to about 125 X 10 F. and a high level of tensile strength over the temperature range from about room temperature or lower up to at least 600 F.

It is likewise within the contemplation of the invention to provide as novel articles of manufacture, resilient elements made from an age hardened nickel-cobalt-ironcolumbium alloy having high strength at elevated temperatures together with an advantageously controlled thermoelastic coefiicient over a temperature range of from room temperature or lower to at least about 600 F., and which is readily fabricated by casting, working, machining, brazing and/or welding.

' Other objects and advantages; will become apparent from the following description taken in conjunction'with the accompanying drawing in which:

FIGURE 1 is a graph comparatively depicting the thermoelast'ic characteristics over a range of temperatures of an alloy of this invention, and those of two commercially available alloys outside of the invention; and

FIGURE 2 is a graphical illustration of the eiiect of positive and negative thermoelast-ic coeificients uponthe resonant frequency of a vibrating element.

Broadly stated, the present invention contemplates alphorus.

4 loys containing specially controlled amounts of nickel, iron, cobalt, columbium,'and titanium. In addition, the alloys also can contain small amounts of tantalum such as are often associated with columbium obtained from commercial sources. These small amounts of tantalum occur in amounts up to, about 20%, e.g., about 1% to about 20% or, more usually, about 5% to about 15%, of the total content of columbium plus tantalum. In percent by weight, the alloys contain at least about 16% nickel and at least about 12.5% cobalt proportioned in correlated amounts according to the relationship or formula V 1.235(%Ni)1+%Co=55.8 to 66.8

columbium with or without small amounts of tantalum in percentages such that the total of the percent columbium plus one-half the percent of any tantalum present is from about 2.4% to about 6%, about 0.5% to about 1.5% titanium, with the balance substantially iron in an amount not less than about 31% of the alloy. In addition to at least 31% iron, the balance of the alloys can also includes up to about 1% aluminum, up to about 1% silicon, up to about 1% manganese, up to about 0.2% carbon, e.g., not more than about 0.1% carbon, up to about 0.1% calcium, and small amounts of incidental elements and impurities normally associated with the alloying, ingredients such as up to about 1% copper, up to about 0.05% sulfur, and up to about 0.05% phos- Elements such as chromium, molybdenum and tungsten are detrimental to the thermoelastic characteristics and while minor amounts of these elements may be present as impurities, the amount of each should be less than 1%. In the alloys of the invention, the maximum nickel content is about 44% and the maximum cobalt content ,is about 47%. 7

With respect to the foregoing relationship, the sum of 1.235 times the percent nickel, plus the percent cobalt in an alloy of the invention is termed the balance index of the alloy. Thus, the foregoing relationship requires that the balance index be in the range of 55.8 to 66.8.

The alloys of the invention can be age hardened by heat treating at temperatures of about 1100 F. to about 1300" F. for about 4 to about 24 hours. In the age hardened condition, the alloys are characterized by high strength, by thermoelastic coeiiicients which are uniform and controlled up to temperatures of at least 600 F., and by metallurgical stability up to at least 1000" F. Advantageously, the alloys are annealed prior to age hardening, a satisfactory annealing treatment comprising heating an,

alloy of the invention to a temperature in the range of about 1400 F. to about 2100 F. for a period of from a few seconds to about five hours. depending upon section thickness and thereafter cooling the alloy sufliciently rapidly to avoid age hardening. An advantageous annealing treatment comprises heating the alloy at a temperature of about 1800 F. to about 1850" F. for about one hour and thereafter water quenching the alloy. The alloys of the invention can be cold worked after annealing and before age hardening and alloys so processed will be referred to hereinafter as cold worked and age hardened alloys, whereas annealed and age hardened alloys which have not been cold worked will be referred to controllable is herein termed the inflection temperature. This term is defined in more detail in the. subsequent discussion of FIGURE 2. The inflection temperatures of the hereinbefore defined alloys are not less than about 600 F.

In carrying the invention into practice, the thermoelastic coefiicients of alloys within the invention are controlled to a major extent by controlling the compositions of the alloys to have balance indexes corresponding to the required thermoelastic coefficients. Thus, where it is necessary to produce an alloy characterized in the annealed and age hudened condition by a low thermoelastic coeilicient, i.e., a thermoeleastic coefiicient of absolute value not greater than about 50 10- F., it is advantageous to control the composition to have a balance index within the range of 60.4 to 66.8. Where it is necessary to produce an alloy characterized in the annealed and age hardened condition by a thermoelastic coefiicient near zero, i.e., a thermoelastic coefiicient of absolute value not greater than about 20 l0* F., it is advantageous to control the composition to have a balance index Within the range of 62.2 to 64.8. When the composition is controlled to have a balance index within these two last mentioned ranges, the inflection temperature of such an alloy of the invention will be at least about 725 F.

Where required, alloys can also be produced in accordance with the invention so as to be characterized in the annealed and age hardened condition by inflection temperatures of not less than about 600 F. and by positive thermoeleastic coefficients in the range of from about 50 10- F. to about 125x 10 F. by controlling the composition to have a balance index in the range of 55.8 to 60.4. Such alloys are advantageous where it is necessary that a structure have increased stillness when the temperature of the structure is increased throughout a range of temperatures, or when it is necessary to compensate for the thermoelasticity of other structures.

More advantageous alloys contain at least about 16% ickel, at least about 24% cobalt, with the nickel and cobalt contents bein controlled to provide a balance index of 62.2 to 64.8, columbium with or without small amounts of tantalum in percentages such that the total percent columbium plus one-half the percent tantalum is from about 2.4% to about 6% of the alloy, about 0.5% to about 1.5% titanium, and the balance substantially iron. The balance of the alloys can also include up to about 1% aluminum, up to about 1% silicon, up to about 1% manganese, up to about 0.1% carbon, up to about 0.1% calcium and the small amounts of incidental elements and impurities referred to hereinbefore. These alloys are characterized in the annealed and age hardened condition by thermoelastic coefficients near zero and infiection temperatures not lower than about 900 F., e.g., 900 F. to 1050 F., and are advantageous for use where an alloy characterized by a thermoelastic coefiicient near zero is required for use in devices which must operate at temperatures up to at least about 900 F.

All alloys of the invention when age hardened are characterized by high strength at room temperature and at elevated temperatures, i.e., these alloys have an ultimate tensile strength at room temperature of at least 125,000 pounds per square inch and a stress-rupture life of at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at900 F. The aforestated alloys of the invention can be produced with higher tensile strength and higher minimum stress-rupture life by advantageously controlling the columbium content or the total of the percent columbium plus one-half the percent tantalum to be from about 3% to about 6%. With the composition thus controlled, the alloys when age hardened within the range of about 1100 F. to about 1300 P. will have a minimum stress-rupture life of not less than about 25 hours at 900 F. and 90,000 psi. and tensile strengths at room temperature of not less than about 150,000 p.s.i. For purposes of maximum strength, the columbuim content or the total of the percent columbium plus one-half the percent tantalum is still more ad- 6. vantageously controlled to be from about 4.5% to about 6%. With the composition thus controlled, the alloys when age hardened in the aforestated temperature range will have a minimum stress-rupture life of about 200 hours at 900 F. and 90,000 p.s.i., and a minimum tensile strength at room temperature of about 175,000 p.s.i.

For the purpose of giving those skilled in the art a better understanding of the invention, the thermoelastic characteristics of an alloy of the invention (Alloy 11) are shown and compared with those of two commercially available alloys (Alloys A and B) in FIGURE 1. Compositions of these alloys and other examples of the invention (Alloys 1 through 10, and 12 through 19) are set forth in Table I. The elastic modulus of Alloy 11 of the invention undergoes far less change in the temperature interval from about F. to about 800 F. than do the elastic moduli of Alloys A and B. The change over this temperature range in the Youngs modulus of Alloy A is about 10.2%, Alloy B about 5.8%, and for Alloy 11 less than 0.1%. Where temperatures exceed about 275 F. the plot of the modulus of Alloy B is particularly non-linear in that the plot has two inflection points, illustrating the fact that the modulus of Alloy B does not vary uniformly with temperature, but instead varies in an inrregular manner which would render compensation difiicult, or even impossible, in devices intended'to operate at temperatures exceeding about 275 F. In contrast, the plot for Alloy 11 is almost a straight horizontal line, indicating that the variation of the Youngs modulus of the alloy of this invention is very small, and that the small variation that does occur is uniform and predictable.

Table I Composition In Weight Percent Alloy N 1 Co Fe 1 Cb+Ta 2 Ti Al C Cr 20. o 33. 4 Bal. 4. 7 0.8 0. 6 0. 02 33. 6 1-1. 7 Bal. 3. 3 0.7 0. 6 0. 01 25. 7 25. 5 132.1. 4. 8 0. 7 0.7 0.02 34. 0 14.8 Bal. 5.1 0.7 0. 6 0.02 33. 4 17. 3 Bal. 5. 2 1. 5 0.6 0.02 20. 7 35.1 132.1. 5.1 0.7 0. 6 0.01 25. 6 30.1 Bal. 5.0 0.6 0.6 0. G2 33. 2 22.1 Bal. 2. 7 1. 5 0. 6 0.02 16. 2 42. 6 Bal. 4. 6 0.6 0. 3 0.02 36. 3 18. 2 Bal. 2. 6 1. 5 0.5 0.02 36.1 18. 2 Bat. 5. 2 0.5 0. 6 0. D1 39. 1 14. 9 Bel. 5. 3 0.7 0. 6 0.01 39. 0 15. 2 Bal. 3. 3 0.7 0.6 0. 02 32. 9 22.1 Bal. 5. 3 0.5 0.6 0.01 20. 4 40. 1 Bal. 5. 2 0.7 0.5 0. 02 33.1 24. 8 Bal. 3. 3 0.7 0. 5 0.02 33. 2 25. 2 Bal. 5. 2 0.7 0. 6 0.01 25. 3 35. 4 Ba]. 5. 1 0. 7 0. 6 0. 01 3G. 1 22. 2 Bal. 5. 4 1. 4 0. 6 O. 01

- Bal. 6.8 1. 0 2. 5 0.8 0.05 42. 5 Bal. 2. 4 0.4 0.02

1 Balance of alloys 1 through 19 includes about 0.5% silicon, 0.4% manganese, 0.03% copper and 0.003% to 0.013% sultur 2 Tantalum is present in these alloys to the extent of about 5% to 15% of the indicated total percent of columbium plus tantalum.

In FIGURE 2 the thermoelastic behavior of alloys throughout a range of temperatures is shown qualitatively to illustrate the determination of inflection temperatures and calculation of the thermoelastic coefiicients of alloys as employed herein. This figure shows two plots of resonant-frequency in transverse vibration against ten perature. The variation of resonant frequency with temperature is indicated in FIGURE 2 in an exaggerated degree for clarity of illustration and is not exemplary of the magnitude of the variations characteristic of alloys of the invention, but the smoothly curved shapes of the plots do illustrate the uniformity of the thermoelastic coefiicients characteristic of alloys of the invention. The upper plot illustrates the characteristics of a uniform positive thermoelastic coefiicient, and the lower plot illustrates a uniform negative coefiicient. It will be noticed that both plots are uniform, i.e., have only slight and substantially constant curvature, up to a point where they exhibit an abrupt change in slope near the high temperature end. The temperature at which the slope of the curve changes abruptly, as at points 1.T., is termed the inflection temperature ('LT.) herein. The term thermoelastic coefficient, as applied herein, refers to the average thermoeiastic coeilicient measured between about 80 F. and the inflection temperature, and is graphically expressed as the slope of a line drawn from the resonant frequency at room temperature to the resonant frequency at the inflection temperature, as shown in the figure. The average thermoelastic coefficient (T.E.C.) is calculated according to the formula where f and f are the resonant frequencies at room temperature and the inflection temperature, respectively, and RT. and LT. are room temperature and inflection temperature in degrees Fahrenheit. In accordance with this formula, the thermoelastic coefficient is in units per degree Fahrenheit. Room temperature, i.e., about 80 F., is used herein as the lower end of the temperature range unless otherwise specified. It should be understood that the same type of determination can be made using other temperatures for the lower end of the range. In referring herein to an alloy as having a thermo-elastic coeflicient of absolute value not greater than a given number up to at least a given temperature, it is meant. unless otherwise indicated, that the above described average thermoelastic coetficient has an absolute (i.e., regard.

less of whether positive or negative) value not greater than the given number, and that the inflection temperature is not lower than the given temperature. Normally, the inflection temperature is the maximum satisfactory operating temperature for a device dependent for satisfactory' operation upon an element having a uniform and controlled thermoelastic coeficient. The alloys of the invention are ferromagnetic at temperatures up to the inflection temperatures of the alloys and are useful in the production of devices which are responsive to, or actuated by, magnetic flux at temperatures up to the inflection temperatures of the alloys.

Thermoelastic coefiicients and inflection temperatures of examples of alloys of the invention and of Alloys A and B were determined by first determining the resonant frequencies at various temperatures ranging from room temperature to about 900 F., and then plotting the results as in the graph of FIG. 2. The resonant frequencies were determined by transversely vibrating a specimen of the alloy at a controlled temperature and measuring the resonant frequency in a test procedure similar to that of Roberts and Northcliffe, as described in Measurement of Youngs Modulus at High Temperatures by M. H. Roberts and J. Northcliffe, published in the Journal of the Iron and Steel lnsttiute, p. 345, November 1947.

The thermoelastic coeiiicients and inflection temperatures of Alloys A and B and of Alloys 1 through 19 of the present invention, all in the heat-treated condition, are set forth in Table II. It is to be noted that although the data in Table II relates to determinations using 80 F. as the low limit of the testing range, the thermoelastic coeificients of alloys of the invention do not change greatly at substantially lower temperatures, e.g., temperatures down to about minus 100 F. or minus 320 F. For example, the thermoelastic coefiicient of Alloy 13 was also determined over the temperatures range of minus 100 F. to 825 F., and found to be about minus 22 l0- F. Alloys suchas Alloys 11 and 12 of Table II are specially advantageous for use where it is desired that an annealed and age hardened alloy be characterized by high strength and by a thernioelastic coefficient very close to zero up to at least about 750 F., and an alloy such as Alloy 9 of Table II is specially advantageous where it is desired 7 that an annealed and age hardened alloy be characterized byhigh strength and by a thermoelastic coefiicient of absolute value not greater than about l0'- F. up

to a temperature of about 1000 F. Alloys such as Table II The thermoelastic coefiicients of Alloys A and B were calculated for the temperature range F. to 800 F. in order to compare the thermoelastic coefficients of these alloys with the thermoelastic coefficient of Alloy 11.

Heat Treatments: Alloys 1 through 191 hour at 1850" R; water quench,.5

hours at 1200 F. Alloy A-Coldworked, 2 hours at 2100 F.-; air cool, 24

hours at 1550" F.; air cool, 20 hours at 1300 F. Alloy BCold worked, 5 hours at 1000 F.

The alloys of the present invention are produced by V melting the ingredients in an induction furnace or any of the other production furnaces employed for similar alloys to result in alloys of the aforestated compositions and then castinginto ingots and hot-forging said ingots, or by casting said alloys as finally shaped castings. Elements such as manganese, slicon, calcium and aluminum can be added to the alloy while molten for purposes of deoxidation, purification, and malleability. Titanium in the alloy also serves these purposes.- Titanium, advantageously about 0.5% to about 1% titanium, and aluminum, advantageously about 0.25% to about 0.75% aluminum, also serve to increase the age hardenability and the strength of the alloy. However, the titanium content should not exceed 1.5% in order to avoid adverse effect upon the ductility and the thermoelastic characteristics of the alloysof the invention. Annealing of forgings or castings at about 1800 F. to 1850 F. is advantageous for purposes of homogenizing the structure and/ or softening the alloy for cold working or machining. Brazing and welding operations are also better performed after annealing. After fabricating operations are complete, age hardening is accomplished as'previously described.

Cold working operations, such as cold rolling, can be The thermoelastic coefiicient of the finished age hardened alloy is principally governed by the composition and the processing steps of age hardening with or without cold working, and these factors are controlled to adjust said coefficient. It should be understood that it is sometimes advantageous to produce an alloy with a coefiicient which is not exactly zero, but which has a controlled positwo or negative value. The alloy composition of this invention is specially designed to provide that the thermoelastic coefficient can be adjusted by a predictable method, this method being to control the amounts of nickel and cobalt so as to adjust the balance index of the alloy. As the balance index is adjusted from 55.8 to 66.8, the thermoelastic coefiicient of an annealed and age hardened alloy of the invention is adjusted proportionately from a value of about plus 125 10 F. to a value of about minus 50 10- F. approximately, i.e., within about plus or minus x10 R, according to the formula where B1. is the balance index. More eXact control of the thermoelastic coefficient can be accomplished by also taking into account our discoveries that additions of titanium up to about 1.5% tend to shift the thermoelastic coeificient slightly in a positive direction and that age hardening at a temperature near the upper limit of the aforementioned range of age hardening temperatures will result in a thermoelastic coefiicient which is more positive (or less negative) than the coeflicient resulting from age hardening near the lower limit of this range. The effect of cold working is to cause the thermoelastic coefficient of the age hardened alloy to be more negative (or less positive) and to increase the inflection tempera ture by a small amount, the magnitude of these efiects being dependent upon the amount of cold work performed. To compensate for the effect of cold Working upon the thermoelastic coeflicient, the age hardening temperature can be adjusted toward the upper limit of the aforementioned range. Also, to compensate for the efiect of cold working upon the thermoelastic coefficient, a compensating heat treatment can be performed on cold worked alloys of the invention between the steps of cold working and age hardening. Such a compensating heat treatment is accompli hed by heating the cold Worked alloy at a temperature of about 1500 F. to 1600" F. for about one hour and then rapidly cooling, e.g., water quenching, the alloy.

in producing a cold worked and age hardened alloy having a thermoelastic coefficient controlled to be equal to a required value, the composition of the alloy is con trolled within the ranges and limits of the invention to result in a balance index which is lower than the balance index of an alloy that would be characterized by the same required thermoelastic coefi'icient after annealing and age. hardening without cold working. Where an alloy of the invention is to be cold Worked to about reduction in area and age hardened at about 12tl0 R, such control is exercised to provide that the finished alloy be characterized by a thermoelastic coefhcient near a required value, i.e., Within about plus or minus 20 10 F. of the required value, by controlling the composition of the alloy to provide that the cobalt content be about 12.5 to about 28% and that the balance index be in the range of about 57 to 65.5 and be of such a value in relation to the required thermoelastic coeflicient as to satisfy the formula Required T.E.C.:1l.6(6l.2-B.l.) X 10 F.

Where it is required to produce a cold worked and age hardened alloy having a thermoelastic coefiicient of absolute value not greater than about 10 F. up to at least about 725 F. when age hardened after cold working an amount up to that equivalent to about 45% reduction in area by cold rolling without performing a compensating heat treatment, it is advantageous to control the composition of an alloy Within the composition of the invention by controlling the cobalt content to be about 12.5% to 28% of the alloy and controlling the amounts of nickel and cobalt to provide that the balance index be in the range of 60.4 to 65.5. The nickel content of such alloys is at least about 26.2%.

As illustrative examples of the elfect of cold working upon the therrnoelastic characteristics of alloys of this invention, the thernioelastic coeificients and inflection tem- 1Q peratures of some of the alloys shown in Table I when in the cold worked and age hardened condition are set forth in Table 111.

Table III Alloy Hear .110. I.T., F.

Treatment X10 /F Heat treatments (after cold rolling) A5 hours at 1200 F. B-l hour at 1500 F.; water quenched, 5 hours at 1200 F. C1 hour at 1600 I 1; Water quenched; 5 hours at 1200 F.

Alloys of Table ill were annealed after hot forging by heat treating at 1800 F. for one hour and water quenching. The alloys were then 44% cold rolled, i.e., cold rolled to a reduction in cross sectional area of about 44%, and heat treated as set forth in the table. such as Alloys 6 and 7 of Table III, heat treated according to heat treatment B, are specially advantageous for use where it is required that a cold rolled and age hardened alloy be characterized by high strength and by a thermoelastic coefficient very close to zero up to at least about 900 F. It will be apparent to one skilled in the art that the alloys of Table IE can be processed to be characterized by thermoelastic coefiicients intermediate the thermoelastic coefficients set forth in Tables 11 and ill by cold working an amount less than'44% cold rolling.

The alloys of the invention are characterized by very useful levels of strength and ductility when age hardened without being cold worked, and the tensile strength is even greater when the alloys have been cold Worked. Tensile properties of examples of age hardened alloys of compositions set forth in Table I are set forth in Table IV, and tensile properties of examples of cold Worked and age hardened alloys of some of the same compositrons are set forth in Table V. Alloys set forth in Tables 1V and V were hot forged, then annealed by heat treating for one hour at 1800 F. to 1850 F. and Water quenching, and thereafter hardened by aging at 1200 F. Alloys set forth in Table V were 44% cold rolled after annealing and before aging.

T able IV Ultimate Yield Elongation, Alloy Tensile Strength Percent Strength, (0.2% Otr- (in 1) p.s.1. set), p.s.i.

191, 000 156, 000 32 g 182, 500 133, 000 18 a 207, 800 157, 000 14 6- 178, 500 137, 000 30 7 191, 500 139, 500 1' 8- 175, 500 122, 000 25 9 164, 560 136, 000 14 10- 178,800 117, 800 29 11 188, 000 122, 500 28 12- 189, 500 128, 000 22 13. 160, 500 106, 000 2a 1=i 186, 000 125, 000 16 15- 189, 500 134, 500 21 16 169, 000 107, 500 28 17- 190, 000 126, 500 22 18. 201, 000 138, 000 19 19 203, 000 141, 000 19 Although the ductility is decreased by cold working, a substantial amount of ductility, i.e., that equivalent to at least about elongation after fracture in a room temperature tensile test, is still present after age hardening when the columbium content is about 2.7% and the alloys have been 44% cold rolled. It is to be noted, however, that ductility in the usual sense, i.e., plastic ductility, is not a requisite for most uses of the alloys of the invention since these alloys will usually be used in structures which are not plastically deformed during use. In some instances, such as in precision instruments, it is an advantage that an elastically operable element which plays a critical role in measuring be made of an alloy in a condition characterized not only by a thermoelastic coeflicient not greater than about 50 10- F., but also by high yield strength and very low plastic ductility. Such an element will have high resistance to plastic deformation, but if it is overstressed, i.e., stressed beyond the elastic limit of the alloy, it will fracture rather than undergo a substantial amount of plastic deformation. This condition is advantageous where it is desirable that, in event of overstressing, a measuring instrument become inoperative rather than continue to operate and produce erroneous measurements. Alloys 3 and 5, of Table V are examples of such alloys in a condition advantageously characterized by high yield strength and low plastic ductility, as well as thermoelastic coeflicients of absolute value not greater than about 50x l0 F. up to temperatures of at least 750 F.

A particularly important advantageous characteristic of alloys of the present invention is that in the age hardened condition these alloys possess a highly useful level of strength at elevated temperatures. As examples, the stress-rupture properties of some of the alloys of the invention shown in Table I, when heat-treated as described for alloys shown in Table IV, are set forth in Table VI.

1 Not ruptured, test discontinued.

The results set forth in Table VI were obtained by stress-rupture testing at the indicated temperatures with a tensile load of 90,000 pounds per square inch. The test specimens of Alloys 4, l2 and .17 did notrupture after about 1000 hours, at which time the test was discontinued.

1 those set forth in Table 1. Specimens were made up in As previously stated, the alloys of this invention also have advantageous characteristics which permit them to be readily fabricated, the characteristic of being adapted to forming by hot working and cold working having been mentioned in regard to some of the foregoing examples of the invention. Brazing is a particularly important process employed in the fabrication of measuring and controlling instruments and other devices in which the alloys of this invention are useful, and it is advantageous that alloys for such instruments and devices be amenable to being brazed by simple methods, i.e., methods requiring neither fluxes nor brazing atmospheres of extreme purity. The alloys of the invention can be readily brazed by simple methods. In evaluating this characteristic, brazing tests were performed by using a simple method for brazing two alloys of the invention, Alloys ll and 19, and two alloys outside the invention, Alloys 7 A and B, these alloys being of compositions similar to the form of T joints and a very small portion of brazing powder was placed in only one place at the joint, and the success of the test was judged by the flow or wetting action along this joint. The brazing powder was one with a nominal composition including 91.2% nickel, 4.5% silicon, and 2.9% boron, with a melting point (in dry hydrogen) of 17.90l800 F. and a flow point of 1820 F. No flux was used. Tests were run in a dry hydrogen atmosphere with a dew point of approximately 65 F. using a brazing temperature of 1900 F. Results of the tests using Alloys 11 and 19 were very good; the flow of brazing metal around the entire joint was complete, forming a uniform bond of excellent appearance. Results of the tests using Alloys A and B were very poor; there was little flow of the brazing material on either Alloy A or Alloy B and the bond was unsatisfactory.

By following the foregoing teachings of the invention, one skilled in the metallurgical art can produce alloys characterized by uniformand controlled thermoelastic coemcients approximately equal to any chosen value from minus 50 l0- F. to x l0 F. up to temperatures of at least 600 PI, e.g., 750 F. or l000 F.,which alloys are also characterized by metallurgical stability and high strength up to temperatures of 900 F. or 1000 F. Since different thermoelastic and mechanical characteristics will be advantageous in various different mechanisms and structures in which alloys of the invention will be utilized, it is to be understood that the skilled metallurgist will practice the invention according to the teachings provided herein to provide the thermoelastic and mechanical characteristics most advantageously suited to his particular needs. The composition for the alloys of the invention having a balance index in the range 55.8 to 66.8 provides for consistently obtaining alloys having uniform thermoelastic coefficients which are amenable to controland which are consistently characterized by high inflection temperatures, ferromaguetism, metallurgical stability and high strength, and which can be readily fabricated by casting, working, machining, brazing and welding.

' Since the alloys in accordance with the invention are uniquely characterized by a controlled thermoelastic coeficient over a temperature range of from room temperature or lower up to about 600 F., or higher, the dis advantages of prior art resilient elements or articles;

such as those mentioned hereinbefore, are overcome. Thus, the present invention is particularly applicable to the production of special resilient metal articles, including springs, pressure sensitive elements, vibratory reeds,

13 e.g., minus 320 R, up to about 600 F. or higher, e.g., 725 F. or 900 F. The invention is also applicable to the processing of special nickel-cobalt-iron-columbium alloys to develop in these alloys the characteristics of high strength and controlled thermoelasticity.

While the present invention has been described as including alloys containing columbium and alloys containing columbium and small amounts of tantalum, the scope of the invention also includes alloys wherein tantalum replaces the columbium in whole or in part. Thus, alloys of the invention can contain up to about 6% columbium and/ or up to about 12% tantalum in proportions such that the total of the percent columbium plus one-half the percent tantalum is from about 2.4% to about 6% of the alloy along with nickel, cobalt, iron and titanium in the aforedescribed proportions. For achieving high strength in tantalum-containin alloys of the invention, it is advantageous that the sum of the percent of any columbium plus one-half the percent of tantalum be from about 3% to about 6%, or more advantageously from about 4.5% to about 6%, of the alloy.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% (30:62.2 to 64.8

with at least about 16% nickel and at least about 24% cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the percent tantalum is from about 4.5% to about 6% of the alloy, with the Weight or" tantalum being from about 1% to about 20% of the total weight of columbium and tantalum in the alto, about 0.5 to about 1.5% titanium, up to about 1% each of silicon, maganese and aluminum, up to about 0.1% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% or" the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coemcent of absolute value not greater than about 20 10 per degree Fahrenheit up to a temperature of at least about 900 F. and by a rupture life of at least 200 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

2. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship with at least about 16% nickel and at least about 24% cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the percent tantalum is from about 3% to about 6% of the alloy, with the weight or" tantalum being from about 1% to about 20% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5% titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.1% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coeiiicient of absolute value not greater than about 20 10 per degree Fahrenheit up to a temperature of at least about 900 F. and by a rupture life of at least 25 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

3. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=62.2 to 64.8

with at least about 16% nickel and at least about 24% cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the percent tantalum is from about 2.4% to about 6% of the alloy, with the weight of tantalum being from about 1% to about 20% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.1% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amoturt not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coefiicient of absolute value not greater than about 20 10" per degree Fahrenheit up to a temperature of at least about 900 F. and by a rupture life of at least 10 hours when subjected to a tensile load of 90,000 square inch at 900 F 4. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the-relationship 1.235 Ni)+% Co=62.2 to 64.8

with at least about 16% nickel and at least about 12.5% cobalt, colurnbium and tantalum in amounts such that the total of the percent colurnbium plus one-half the percent tantalum is from about 2.4% to about 6% of the alloy, with the weight of tantalum beingfrom about 1% to about 20% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less'than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coefficient of absolute value not greater than about 20 10- per degree Fahrenheit up to a temperature of at least about 725 F. and by a rupture life of at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

5. A coldworkable, age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=60.4 to 65.5

with about 12.5% to about 28% cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the percent tantalum is from about 4.5% to about 6% of the alloy, with the weight of tantalum being from about 1% to about 20% of the total Weight of columbium and tantalum in the alloy, about 0.5 to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% or" the alloy, said alloy being characterized in the cold worked and age hardened condition, where the amount of cold work has not exceeded that equivalent to about 45% reduction in area, by a uniform and controllable thermoelastic coetficient of absolute value not greater than about x10 per degree Fahrenheit up to a temperature of at least 725 F. and by a rupture life of at least about 200 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

6. A cold-workable, age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship pounds per 5 6 1.235 Ni)+% Co=60.4 to 65.5

a silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the cold Worked and age hardened condition, where the amount of cold work has not exceeded that equivalent to about 45 reduction in area, by a uniform and controllable thermoelastic coefiicient of absolute value not greater than about 50x10- per degree Fahrenheit upv to a temperature of at least 725 F. and by a rupture life of at least about 25 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

f 7. A cold-workable, age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=60.4 to 65.5

with about 12.5% to about 28% cobalt, columbium and tantalum in amounts such that the total. of the percent columbium plus one-half the percent tantalum is from about 2.4% to about 6% of the. alloy, with the weight of tantalum being from about 1% to about 20% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5% "titanium, up to about 1% each of silicon, manganese and aluminum, upto about 0.2% carbon, less than 1% each of chromium, tungsten and molydenum, and the balance essentially iron in an amount not less than about, 31% of the alloy, said alloy being characterized in the cold worked and age hardened condition, where the amount of cold work has notexcee ded that equivalent to about 45% reduction in area, by a uniform and controllable thermoelastic coeificient of absolute value not greater than about 50x10 per degree Fahrenheit up to a' temperature of at least 725 F. and by a rupture life of at least aboutlO hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F. V

'8. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 7 1.235 Ni)+% 06:60.4 [0 66.8 r with at least about 16% nickel and at least about 12.5%

' cobalt, columbium and tantalum in amounts such that the total of the percent columbium plu one-halt the percent tantalum'is from about 4.5% to about 6% of the alloy, with the weight of tantalum being from about 1% to about 20% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5% titanium, up to of silicon, manganese and alum'mum, up to about 0.2% carbon,.less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniformand controllable thermoelastic coefiicient of absolute value not greater than about 50 10- per degree Fahrenheit up to a temperature of at least about 725 F. and by a rupture life of at least 200 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F. V

. 9. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts acabout 1% each cording to the relationship 1.235 Ni)+% 06:60am 66.8 with at least about 16% nickel and at least about 12.5%

cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the perto about of thetotal weight of columbium and tantalum in the alloy, about 0.5 to about 1.5% titanium, up to about 1% each of silicon, manganese and aluminum,

up to about 0.2% carbon, less than 1% each of chromium,

tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy,

said alloy being characterized in the annealed and age.

hardened condition by a uniform and controllable thermoelastic coeflicient of absolute value not greater than about 50x10 per degree Fahrenheit up to a temperature of at 600 F. and by a rupture to about 20% least about 725 F. and by a rupture life of at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

10. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amountsaccording to the relationship 1.235 Ni)-l% Co:55.8 to 60.4

1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than'1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coefficient of positive value in the range of from about 50 10- per degree Fahrenheit to about X 10 per degree lifeof at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F. a

11. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amoimtsaccording to the relationship I 1.235 Ni)+% 06:65.8 to 66.8

the total of the percent columbium plus one-half the percent tantalum is from about 4.5% to about 6% of the alloy, with the weight of tanalum being from about 1% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganeseand aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungstenand molybdenum, and the'b'alance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the: annealed and age hardened condition by a uniform and controllable thermoelastic coefficient in the range of from minus 50 10 per degree Fahrenheit to about plus 125 X 10- per degree Fahrenheit up to a temperature of at least about 600 F. and by a rupture life of at least 200 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

12. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=55.8 to 66.8

with the Weight of tantalum being from about 1% to about Fahrenheit up to a temperature of at, least about 20% of the total weight of columbium and tantalum in the alloy, about 0.5 to about 1.5% titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic co efficient in the range of from minus 50X 10 per degree Fahrenheit to about plus 125 10 er degree Fahrenheit up to a temperature of at least about 600 F. and by a rupture life of at least 25 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

13. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% CO=55.8 to 66.8

with at least about 16% nickel and at least about 12.5 cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the percent tantalum is from about 2.4% to about 6% of the a lo with the weight of tantalum being from about 1% to about 20% of the total Weight of columbium and tantalum in the alloy, about 0.5 to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromiurn, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coefficient in the range of from minus 50X 10 per degree Fahrenheit to about plus 125 X 10 per degree Fahrenheit up to a temperaure of at least about 600 F. and by a rupture life of at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

14. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=55.8 to 66.8

with at least about 16% nickel and at least about 12.5 cobalt, columbium and tantalum in amounts such that the total of the percent columbium plus one-half the percent tantalum is from about 2.4% to about 6% of the alloy, with the weight of tantalum being from about 1% to about 20% of the total weight of columbium and tantalum in the alloy, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron, With the iron content being at least 31% of the alloy.

15. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship.

1.235 Ni)+% Co=55.8 to 66.8

with at least about l6% nickel and at least about 12.5 cobalt, up to about 6% columbium, up to about 12% tantalum, 'ith the total of the percent columbium plus one-half the percent tantalum being from about 4.5% to about 6% of the alloy, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% or" the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coeflicient in the range of from minus 50X 10* per degree Fahrenheit to about plus 125x l0 per degree Fahrenheit up to a temperature of at least about 600 F. and by a rupture life of at least 200 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

18 16. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=55.8 to 66.8

with at least about 16% nickel and at least about 12.5 cobalt, up to about 6% columbium, up to about 12% tantalum, with the total of the percent columbium plus one-half the percent tantalum being at least about 2.4% but not exceeding about 6% of the alloy, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coeflicient in the range of from minus 50 10 per degree Fahrenheit to about plus l25 10 per degree Fahrenheit up to a temperature of at least about 600 F. and by a rupture life of at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

17. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=62.2 to 64.8

with at least about 16% nickel and at least about 24% cobalt, about 4.5% to about 6% columbium, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.1% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being characterized in the annealed and age hardened condition by a uniform and controllable thermoelastic coefiicient of absolute value not greater than about 20 10- per degree Fahrenheit up to a temperature of at least about 900 F. and by a rupture life of at least 200 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

18. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts ac cording to the relationship 1.235 Ni)+% Co=55.8 to 66.8

with at least about 16% nickel and at least about 12.5 cobalt, about 2.4% to about 6% columbium, about 0.5 to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron in an amount not less than about 31% of the alloy, said alloy being charac terized in the annealed and age hardened condition by a uniform and controllable thermoelastic coefiicient in the range of from minus 50 10- per degree Fahrenheit to about plus X 10* per degree Fahrenheit up to a temperature of at least about 600 F. and by a rupture life of at least 10 hours when subjected to a tensile load of 90,000 pounds per square inch at 900 F.

19. An age-hardenable alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 Ni)+% Co=55.8 to 66.8

with at least about 16% nickel and at least about 12.5% cobalt, about 2.4% to about 6% columbium, about 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less 1% each of chromium, tungsten and molybdenum, and the balance essentially iron, with the iron content being at least 31% of the alloy.

20. A process for producing an alloy characterized by high strength and a uniform and controlled thermoelastic coefficient of absolute value not lower than about minus 513x10 per degree Fahrenheit and not greater than with at least about 16% nickel and at least about 12.5% cobalt, up to about 6% colurnbium, up to about 12% tantalum, with the totalof the percent colunlbium plus one-half the percent tantalum being from about 2.4% to about 6% of the alloy, about 0.5% to about 1.5% titaniurn, up to about 1% each of silicon, manganese and aluminum, up to about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron, with the iron content being at least 31% of the alloy, but working said ingot to produce a hotworked all y, annealing the ho'tworked alloy by heating said alloy for a period of a few seconds to about five hours at a temperature in the range of about 1400 F.

' to about 2100 F. and rapidly cooling the thus heated alloy from said temperature, and thereafter age hardening the annealed alloy at a "temperature of from about 1100 F. to about 1300 F. for'about 4 hours to about 24 hours. 7

21. A process for producing a cold-worked alloy characterized by high strength and a uniform andcontrolled thermoelas'tic coetiieient of absolute value not greater than about 50X 1()' per degree Fahrenheit up to a temperature ofat least about 725 F. comprising the steps of providing an ingot of an alloy consisting essentially of nickel; and cobalt proportioned in correlated amounts accordingto the relationship 1.235 (%Ni) +%Co=60.4 to 65.5

with about 12.5% to about 28% cobalt, up to about 6% columbiurn, up to about 12% tantalum, with the total of the percent col'umbium plus one-half -the percent tantalum being from about 2.4% to about 6% of the alloy, about 0.5 to about 1.5% titanium, up to about 1% each of silicon, manganese and aluminum, up to'about 0.2% carbon, less than 1% each of chromium, tungsten and molybdenum, and the balance essentially iron with the iron content being at least 31% of the alloy, hot working said ingot to produce a hot-worked alloy, annealing the hot-worked alloy by heating said alloy for a period of a few seconds to about five hours at a temperature in the range of about 1400 F. to about 2100 F. and rapidly cooling the thus heated allo'y from said temperature, cold working theannealed alloy an amount not greater than that equivalent to about reduction in area by cold rolling, and thereafter age hardening the cold-worked alloy at a temperature of from about1100 F. to about 1300 F. for about 4 hours to about 24 hours.

22. A resilient metal article subjected in use to dilfering temperatures within the range of from about minus 320 F. to about 600 F. characterized when in use within said range by ferromagnetism and by a uniform and controlled thermoelastic coefficient not lower than about minus 10 per degree'Fahrenheit and not greater than about x10- per degree Fahrenheit and by a rupture life of at least 10 hours at a stress of 90,000 pounds per square inch at 900 F. and made of an alloy consisting essentially of nickel and cobalt proportioned in correlated amounts according to the relationship 1.235 (%Ni) +%Co=55.8 to 66.8

with at least about 16% nickel and at least about 12.5% cobalt, up to about 6% columbium, up to about 12% tantalum, with the total of the percent columbium plus one-half the percent tantalum being from about 2.4% to about 6% of the alloy, 0.5% to about 1.5 titanium, up to about 1% each of silicon, manganese and aluminum,

up to about 02% carbon, less than 1% each of chromium,

References Cited by the Examiner UNITED STATES PATENTS 2,018,520 10/35 Halliwell l48-1 62 X 2,044,165 6/36 'Halliwell 148162 X 2,116,923 5/38 Bolton 148-162 X 2,773,762 12/56 Dubois et al. 750-4343 DAVID L. RECK, Primary Examiner,

STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,157,495 Noyemb'enl'i 19 4 Herbert L, Eiselstein et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 22, for "includes" read include column 7, line 3, after "temperature", the single quotation mark should be a double quotation mark; line 25, for "thermoelastic" read thermoelastic line 27, for "meant," read meant, line 54, for "Insttiute" read Institute same column 7, line 65, for "temperatures" read temperature column 8, Table II, heading to the second column, line 1 thereof, after "T.E.,C," insert a comma; same column 8, line 40, for "slicon" read silicon column 10, Table III, heading to the second column, line 1 thereof, for "Hear" read Heat same Table III, heading to the third column, line 1 thereof, after "T.E.C." insert a comma; same Table III, third column, line 18 thereof, for "-3" read -30 same column 10, Table IV, fourth column, line 14 thereof, for

"16" read 21' line 1'5 thereof, for "21" read l6 column 11, line 70, for "The" read Test column 13, line 43, for "maganese" read 'manganese column 15, line 54, for "plu" read plus column 16, line 51, for "tanalum" read tantalum column 18, line 15, after "than" insert about same column 18, line 68, after "less" insert than Signed and sealed this 13th day of April 1965,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. AN AGE-HARDENABLE ALLOY CONSISTING ESSENTIALLY OF NICKEL AND COBALT PROPORTIONED INCORRELATED AMOUNTS ACCORDING TO THE RELATIONSHIP 1.235 (%NI)+% CO=62.2 TO 64.8 